Ims inbound roamer and short number dialing

ABSTRACT

Network nodes for an access network and a home network of a first UE are described for use when routing an originating call from the first UE in the access network including an IMS network. A network node receives a SIP INVITE message associated with the originating call from the first UE, and including a called party number associated with the call. It determines whether the first UE is visiting the access network and whether the called party number is associated with the access network. A query to a database is performed, the database comprising a plurality of called party numbers, as to whether the called party number is allowable for use in the access network when the UE is visiting and when the called party number is associated with the access network. Instructing the home network to route the originating call to the access network when a response from the query indicates the called party number is allowable for use in the access network. The home network receives the instruction and routes the originating call to the access network for further processing.

TECHNICAL FIELD

The present invention relates to methods and apparatus for routing anoriginating call in a telecommunications network including an InternetMultimedia Subsystem (IMS) network. In particular, the invention relatesto methods and apparatus for routing the originating call of an inboundroamer to the access network when the called party number is allowablefor use in the access network.

BACKGROUND

IP Multimedia services provide a dynamic combination of voice, video,messaging, data, etc. within the same session. By growing the number ofbasic applications and the media which it is possible to combine, thenumber of services offered to the end subscribers will grow, and theinter-personal communication experience will be enriched. This will leadto a new generation of personalised, rich multimedia communicationservices, including so-called “combinational IP Multimedia” services.

IP Multimedia Subsystem (IMS) is the technology defined by the ThirdGeneration Partnership Project (3GPP) and ETSI TISPAN group to provideIP Multimedia services over mobile communication networks. IMS provideskey features to enrich the end-subscriber person-to-person communicationexperience through the use of standardised IMS Service Enablers, whichfacilitate new rich person-to-person (client-to-client) communicationservices as well as person-to-content (client-to-server) services overIP-based networks. The IMS makes use of the Session Initiation Protocol(SIP) to set up and control calls or sessions between subscriberterminals (or subscriber terminals and application servers). The SessionDescription Protocol (SDP), carried by SIP signalling, is used todescribe and negotiate the media components of the session. Whilst SIPwas created as a subscriber-to-subscriber protocol, IMS allows operatorsand service providers to control subscriber access to services and tocharge subscribers accordingly.

By way of example, FIG. 1 a illustrates schematically atelecommunications network showing an example of the IMS networkarchitecture used for roaming users when they place a call in a VisitedPublic Land Mobile Network (V-PLMN). In this example, a calling party Ais visiting the V-PLMN for party A (V-PLMN A or Visited operator forparty A) places a call to a called party B visiting V-PLMN for party B(V-PLMN B). Each PLMN includes some IMS architecture such asInterconnection Border Control Function (IBCF) or Translation Gatewaynodes (TrGw) that connect the PLMN with each other via core networks forexample those based on Internetwork Packet Exchange (IPX) 1, 2, 3, and4. An IBCF is an interconnecting gateway between an IMS network 102 andother IP networks e.g. another IMS networks or core networks etc. EachPLMN includes some IMS architecture such as registrar nodes associatedwith the various access domains (or networks) such as Call/SessionControl Functions (CSCFs), which operate as SIP proxies within the IMS.The 3GPP architecture defines three types of CSCFs: the Proxy CSCF(P-CSCF) which is the first point of contact within the IMS for a SIPterminal i.e. calling party A; the Serving CSCF (S-CSCF) (not shown)which provides services to the subscriber that the subscriber issubscribed to; and the Interrogating CSCF (I-CSCF) whose role is toidentify the correct S-CSCF and to forward to that S-CSCF a requestreceived from a SIP terminal via a P-CSCF.

Within the IMS network architecture, Application Servers (ASs) areprovided for implementing IMS service functionality. ASs provideservices to end users in an IMS system, and may be connected either asend-points over the 3GPP defined Mr interface, or “linked in” by anS-CSCF over the 3GPP defined ISC interface. In the latter case, InitialFilter Criteria (IFC) are used by an S-CSCF to determine which ASsshould be “linked in” during a SIP Session establishment (or indeed forthe purpose of any SIP method, session or non-session related). The IFCsare received by the S-CSCF from a home subscriber server (HSS) duringthe IMS registration procedure as part of a user's or subscriber'sSubscriber Profile.

The user equipment (UE) for a calling or called party may comprise orrepresent any device used for communications. Examples of user equipmentthat may be used in certain embodiments of the described network arewireless devices such as mobile phones, terminals, smart phones,portable computing devices such as lap tops, handheld devices, tablets,netbooks, computers, personal digital assistants and other wirelesscommunication devices, or wired communication devices such astelephones, computing devices such as desktop computers, set-top boxes,and other fixed communication devices.

When the calling party A (UE A) places a call to the called party B (UEB) the call set-up process involves an originating call associated withUE A and a terminating call associated with UE B. The terms “originatingcall” and “terminating call” may comprise or represent the connectionset-up signalling in relation to UE A or UE B, respectively. Examples oforiginating or terminating calls that may be used in certain embodimentsof the described network include, but are not limited to, the connectionset-up signalling enabling a communication connection to be made betweenUE A and UE B in the two call halves model. The originating call is theconnection set-up signalling for UE A in the first call half and theterminating call is the connection set-up signalling for connecting thecall with UE B in the second call half.

When the calling party A originates a call, the basic procedure involvesthe P-CSCF of the V-PLMN A receiving the originating call and routingthe call from V-PLMN A to the Home PLMN for party A (H-PLMN A or Homeoperator for A party) via the corresponding IBCF/TrGWs. Generally, theH-PLMN or home network identifies the PLMN or network in which theprofile of a user such as calling party A or called party B (e.g. asubscribers profile) is held. The H-PLMN A routes the originating callto the H-PLMN B based on the call number (B number) indicated in theoriginating call. Since the call number relates to a called party B inanother network, the H-PLMN A routes the originating call to H-PLMN B(Home operator of B party) and it is then routed to V-PLMN B (Visitedoperator of B party), where the C-CSCF of V-PLMN B forwards the call tothe called party B. The media is “anchored” in every network that theoriginating call traverses, i.e. follows the path of the call i.e. acall chain.

During the call routing procedure, the H-PLMN A may perform so-callednumber normalisation. In non-roaming cases, when calling party A placesa call based on the H-PLMN A numbering plan using short numbers (e.g.08-71912345 instead +46871912345), then H-PLMN A performs the necessarynumber conversion in-order to correct the number format according itsown numbering plan. In another example, when calling party A is notroaming and dials a service number (e.g. 118118), as this number isrecognised as a home service number, then the call is routed to therelevant HPLMN A service or servicer operator.

According to 3GPP Technical Standard 23.228 “IMS” Stage 2 Release 11 andother 3GPP Standards, even if the calling party A is roaming, the H-PLMNA IMS network will be within the call chain for all calls. This meansthat if calling party A is an IMS (e.g. VoLTE) roamer in VPLMN-A, thenwhen calling party A dials a short number according to the dialing planof VPLMN-A. For example, such calls may include when calling party Atries to call a called party B within the same visited network using alocal number format (e.g. an inbound roamer from Germany in Sweden,dials 08-719 12345 to reach somebody in Sweden). Alternatively, callingparty A (an inbound roamer) may dial a service number in the V-HPLMN A(e.g. #TAXI to get to closest taxi company in the visited network).

However, based on current IMS routing procedures, the originating callof calling party A will be routed to HPLMN-A and particularly to an IMSApplication Server and multimedia telephony service (MMTel) AS (notshown) within H-PLMN A. However, since the intention of the callingparty A is unknown to H-PLMN A, then an incorrect routing of the callmay result due to overlapping service numbers (e.g. same service numbersare used for different purposes in H-PLMN A and V-PLMN A).Alternatively, the call may simply fail due to the number being based ona local numbering plan in the V-PLMN A, which may be unknown to theH-PLMN A network.

Therefore, there is a significant need to optimise handling oforiginating calls in a telecommunications network including an IMSnetwork to minimise or even eliminate incorrect or failed routing oforiginating calls from inbound roaming users.

SUMMARY

It has been recognised here that whilst there are certain mechanisms forrouting an originating call from an access network the calling party isvisiting towards a called party or service within the access network,none of the relevant standards or systems allow for the access networkto flexibly route calls dialed with non-standard format numbers. Inparticular, at present, the relevant standards do not provide anymechanisms that enable a user or calling party originating a call or anaccess network the user is visiting (e.g. a VPLMN of calling party A) toflexibly route the originating call towards a service or called partywithin the access network. It is an object of the present invention toprovide methods and apparatus of routing an originating call from afirst UE roaming in an access network of a telecommunications networkcomprising an IMS network to allow the originating call to be routed tothe correct called party, when the called party number is allowable foruse in the access network, thereby optimising quality of service withinthe network.

According to a first aspect of the invention there is provided a methodof routing an originating call from a first UE in an access networkcomprising an IMS network in which the IMS network includes a networknode, the method, performed by the network node. The network nodereceives a SIP INVITE request message associated with the originatingcall from the first UE, the SIP INVITE request message including acalled party number associated with the call. The network nodedetermines whether the first UE is visiting the access network andwhether the called party number is associated with the access network.The network node queries a database, the database comprising a pluralityof called party numbers, as to whether the called party number isallowable in the access network when the UE is visiting the accessnetwork and when the called party number is associated with the accessnetwork. The network node instructs a home network of the first UE toroute the originating call to the access network when a response fromthe query indicates the called party number is allowable for use in theaccess network.

As an option, determining whether the first UE is visiting the accessnetwork further includes determining whether the first UE is IMSregistered. Alternatively or in addition to, determining whether thefirst UE is visiting the access network further includes determiningwhether the home network is known to the network node. As anotheroption, determining whether the called party number is associated withthe access network further includes determining that the called partynumber is representative of a short code number or a short number.

Optionally, where the plurality of called party numbers include aplurality of service numbers, and the database includes policiesindicating whether the plurality of service numbers are allowable foruse in the access network, then determining from the database furtherincludes: triggering the database to indicate whether the called partynumber is allowable for use in the access network based on the policies;and receiving a response from the database indicating whether the calledparty number is allowable for use in the access network.

As an option, the method may include determining, from the receivedresponse from the database, whether the called party number is allowablefor use in the access network, and instructing the home network of thefirst UE to route the originating call to the access network when it isdetermined that the called party number is allowable for use in theaccess network. The step of determining whether the called party numberis allowable for use in the access network may further compriseanalysing or interpreting the received response from the database todetermine whether the called party number is allowable for use in theaccess network.

As another option, instructing the home network further includes:modifying the received SIP INVITE request message to set a phone contextparameter to the access network domain name when the called party numberis allowable for use in the access network; and transmitting themodified SIP INVITE request message towards the home network.Optionally, the phone context parameter is within the Request-UniformResource Identifier (R-URI) of the SIP INVITE request message.

As an option, instructing the home network further includes modifyingthe received SIP INVITE request message to set a routing indication forrouting the originating call from the home network to the access networkwhen the called party number is allowable for use in the access network.Additionally, modifying the SIP INVITE request message further includesmodifying the R-URI of the SIP INVITE request message to set the routingindication. As a further option, the network node includes thefunctionality of a proxy call session control function or thefunctionality of an interconnection border control functions.

According to a second aspect of the invention, there is provided anetwork node for routing an originating call from a first UE in anaccess network comprising an IMS network. The network node including areceiver, a transmitter, a memory unit, and processing logic, where theprocessing logic is connected to the receiver, to the transmitter, andto the memory unit. The receiver is configured to receive a SIP INVITErequest message associated with the originating call from the first UE,the SIP INVITE request message including a called party numberassociated with the call. The processing logic includes determininglogic configured to determine whether the first UE is visiting theaccess network and to determine whether the called party number isassociated with the access network. The processing logic furtherincludes query logic configured to query a database, the databasecomprising a plurality of called party numbers, as to whether the calledparty number is allowable in the access network when the determininglogic determines that the first UE is visiting the access network andthat the called party number is associated with the access network. Thetransmitter is configured to send the query to the database. Theprocessing logic and the transmitter are further configured to instructa home network of the first UE to route the originating call to theaccess network when a query response from the database indicates thatthe called party number is allowable for use in the access network.

As an option, the determining logic is further configured to determinewhether the first UE is IMS registered for use in determining whetherthe first UE is visiting the access network. Alternatively oradditionally, the determining logic is further configured to determinewhether the home network is known to the network node when the first UEis determined to be visiting the access network. As another option, thedetermining logic for determining whether the called party number isassociated with the access network is further configured to determinethat the called party number is representative of a short code number ora short number.

Optionally, where the plurality of called party numbers include aplurality of service numbers, and the database includes policiesindicating whether the plurality of service numbers are allowable foruse in the access network, the transmitter and query logic are furtherconfigured to trigger the database to indicate whether the called partynumber is allowable for use in the access network based on the policies.The receiver logic and the processing logic are further configured toreceive a response from the database indicating whether the called partynumber is allowable for use in the access network.

Optionally, the determining logic may be further configured todetermine, from the received response from the database, whether thecalled party number is allowable for use in the access network. Theprocessing logic and the transmitter may be further configured toinstruct the home network of the first UE to route the originating callto the access network when the determining logic indicates that thecalled party number is allowable for use in the access network. Thedetermining logic may be configured to analyse or interpret the receivedresponse from the database to determine whether the called party numberis allowable for use in the access network.

As an option, the processing logic is further configured to instruct thehome network by modifying the received SIP INVITE request message to seta phone context parameter to the access network domain name when thecalled party number is allowable for use in the IMS network. Thetransmitter is further configured to instruct the home network bytransmitting the modified SIP INVITE request message towards the homenetwork. Optionally, the phone context parameter is within the R-URI ofthe SIP INVITE request message.

As another option, the processing logic is further configured toinstruct the home network by further modifying the received SIP INVITErequest message to set a routing indication for routing the originatingcall from the home network to the access network when the called partynumber is allowable for use in the access network. Alternatively oradditionally, the processing logic (308) is further configured to modifythe R-URI of the SIP INVITE request message to set the routingindication. As a further option, the network node includes thefunctionality of a proxy call session control function or thefunctionality of an interconnection border control functions.

According to a third aspect of the invention, there is provided a methodof routing an originating call from a first UE in an access networkincluding a first IMS network towards a home network including a secondIMS network. The first IMS network including a first network node in anaccess network the first UE is visiting. The second IMS networkincluding a second network node in a home network of the first UE. Themethod, performed by the second network node, includes receiving a SIPINVITE request message associated with the originating call from thefirst UE in the visited access network. The SIP INVITE request messageincluding a called party number associated with the call and anindication that the called party number is allowable for use in thevisited access network. Detecting the indication within the received SIPINVITE request message that the called party number is allowable for usein the visited access network. Transmitting the SIP INVITE requestmessage towards the visited access network.

According to a fourth aspect of the invention, there is provided anetwork node for use in routing an originating call from a first UE inan access network coupled to a first IMS network towards a home networkincluding a second IMS network. The first IMS network includes a firstnetwork node associated with the access network the first UE isvisiting. The second IMS network includes the network node, which isassociated with a home network of the first UE. The network nodecomprising a receiver, a transmitter, a memory unit, and processinglogic, the processing logic being connected to the receiver, to thetransmitter, and to the memory unit. The receiver is configured toreceive a SIP INVITE request message associated with the originatingcall from the first UE in the visited access network. The SIP INVITErequest message including a called party number associated with the calland an indication that the called party number is allowable for use inthe visited access network. The processing logic is configured to detectthe indication within the received SIP INVITE request message that thecalled party number is allowable for use in the visited access network.The transmitter and processing logic are configured to transmit the SIPINVITE request message towards the visited access network.

The invention provides the advantages of allowing the IMS network(s) tointroduce functionality to allow IMS inbound roamers to call localcalled party numbers while at the same time minimizing the impact ofdeployment on network operators and the existing IMS infrastructure.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more fully understood, some of theembodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 a is a schematic illustration for IMS routing of an originatingcall of roaming calling party A;

FIG. 1 b is a schematic illustration of another example IMS network forrouting an originating call according to the invention;

FIG. 1 c is a schematic illustration of an arrangement for a networknode according to the invention to interface with a database;

FIG. 2 a is a flow diagram illustrating a process for routing anoriginating call according to embodiments of the invention;

FIG. 2 b is a flow diagram illustrating a process for whether thecalling party is an IMS roamer according to embodiments of theinvention;

FIG. 2 c is a flow diagram illustrating a process for determiningwhether the called party number is allowable according to embodiments ofthe invention;

FIG. 2 d is a schematic illustrating the various levels of modificationthat may be applied to a SIP INVITE request message for use in routingthe originating call according to embodiments of the invention

FIG. 2 e is a flow diagram illustrating a process in a home network forrouting an originating call according to embodiments of the invention

FIG. 3 a is a schematic diagram of a network node according toembodiments of the invention.

FIG. 3 b is a schematic diagram of another network node according toembodiments of the invention.

DETAILED DESCRIPTION

In order to overcome the problems identified above there will now bedescribed methods and apparatus for routing an originating call of anIMS roaming user of an access network such as a VPLMN towards the homenetwork (e.g. a H-PLMN) of the IMS roaming user based on whether theaccess network identifies the called party number is allowable for usein the access network.

As described previously, in most cases, based on current IMS routingprocedures, an originating call from an IMS roaming user (e.g. callingparty A) in a V-PLMN for calling party A will automatically be routed tothe H-PLMN of the calling party A, which determines where the callshould be routed. However, the H-PLMN A IMS AS or MMTel AS do not knowthe intention of the user of the calling party A's UE. For example, if aservice number was dialed, did the user want a home service number or avisited service number? Although there is an optional function in theIR.92 standard entitled “IMS Profile for Voice and SMS” for a UE to setcertain indicators in SIP signaling to indicate if the calls are for alocal service/number or a home service/number, this kind of functionneeds to be set by a user, is not considered reliable nor readilyavailable in all UEs.

Currently, when a called party number based on local numbering plan in aVPLM has been dialed by an IMS roamer, then it is most likely that theHPLMN IMS network will not be able to perform correct called partynumber normalization because its roaming partners numbering plans (thereare hundreds of these) may be unknown. In any event, if the servicenumber corresponds to one in the VPLMN, the HPLMN would not be able toexecute the service and the call will fail. Alternatively, if there areoverlapping service numbers (e.g. same service number with differentpurposes in HPLMN and VPLMN) when the originating call reaches theHPLMN, the service in the HPLMN will be used and there no efficient orreliable way for an IMS inbound roamer to use the services of the VPLMN.

In order to address the problems identified, it is proposed to introducean interface between IMS network nodes such as the P-CSCF (or IBCF) anda database (e.g. an external database) comprising a plurality of calledparty numbers that are allowable for use in the VPLMN. This interfaceallows a mechanism to be implemented, or a process to be executed, inthe IMS network node that allows it to detect and distinguish the localnumbers such as local service numbers in originating calls from IMSroaming UEs or calling party UE's (e.g. IMS inbound roamers).

For example, when an IMS inbound roamer dials a service number, based onpolicy a trigger to the database can be executed to resolve the natureof the dialed number. Based on the response from the database,additional steps for correction of the dialed number may be taken in theIMS network node to enable correct handling of the originating call.This may involve manipulating the SIP signaling (e.g. modifying the SIPINVITE request message) in relation to the originating call. As anexample, the SIPINVITE request message body or header may be modified.If the SIP INVITE request message header is modified, this may entailmodifying the Request-URI.

As an example of the mechanism according to the invention, a networknode (e.g. P-CSCF or IBCF) may perform the following actions as part ofa call set-up procedure.

-   1. The network node may identify whether the calling party    originating the call is an inbound roamer. IMS inbound roamers will    have performed an IMS registration (3GPP TS 24.229) toward its home    IMS domain or H-PLMN with a domain name that does not belong to the    VPLMN. The network node may be configured to recognize this    different domain name. When the network node includes the    functionality of a P-CSCF, then it will recognize the different    domain name. If the originating call is identified to be in the same    domain name as the VPLMN, then the calling party is not an IMS    inbound roamer and the call is handled in the normal fashion; and-   2. Once the network node has identified that the calling party is an    IMS inbound roamer, the network node then determines whether the    user dialed a short code/short number or any other non-normalised    called party number, i.e. the dialed number is not in the    international format (e.g. does not start with a ‘+’ as in    ‘+4681253436’.

In addition, the network node may also identify whether the node isconfigured for performing a roaming control. If it is not, then it mayforward the originating call to a network node that is configured forperforming roaming control.

Once actions 1 and 2 have been undertaken, the network node for calledparty numbers passing the above criterion trigger a database provisionedwith called party numbers that are useable within the access network todetermine whether the called party number is useable in the accessnetwork.

The network node may also be configured with a pre-configured filter tocapture specific called party numbers (e.g. service numbers according toa local dial plan), and then trigger the database accordingly. This mayreduce the number of originating calls that should be routed by themechanism according to the invention.

The database may be provisioned with called party numbers such asservice numbers that are allowed to be used by the inbound roamer in thecurrent access network (V-PLMN). This may be due to a roaming agreementbeing in place between the H-PLMN of the calling party and the V-PLMN).This will also capture service numbers that are in conflict in theV-PLMN and H-PLMN and based on the agreement, a response is sent to thenetwork node to instruct the network node how the called party numbershould be treated.

FIG. 1 b provides a schematic illustration of the IMS networkarchitecture 100 comprising a V-PLMN 101 and H-PLMN 102 for implementinga process/mechanism according to the invention in an network node 103having P-CSCF functionality and/or IBCF functionality. The V-PLMN 101includes UE A 104, an IMS inbound roamer, in which in step A, the userof UE A 104 dials called party number (e.g. 133) when in the V-PLMN 101to reach a local service located within the V-PLMN 101. Currently,without the mechanism/processes according to the invention, such a callwill be routed to H-PLMN 102 and will fail or connect to the home based133 service.

On dialing the called party number, UE A 104 originates a call bysending a SIP INVITE request message, the SIP INVITE request messageincludes the called party number (e.g. 113) and the phone-contextparameter set to the domain name of the H-PLMN (e.g.hplnmn.com@hplmn.com) because UE A 104 will have performed an IMSregistration toward its home IMS domain or H-PLMN 102, and so uses theH-PLMN 102 domain name (e.g. hplnmn.com@hplmn.com).

On receiving the SIP INVITE request message, the network node 103 thatis within V-PLMN 101 performs a process according to the invention basedon a detection and routing control function. The detection and routingcontrol function applies the above actions 1 and 2 and recognizes thatthe called party number is a service number from a call originated by anIMS inbound roamer (e.g. the service number matches the “filter”) or anyother called party number that is not used for an international callwith an international prefix. The detection and routing control functionperforms a query to access or trigger a database 105 to determinewhether the called party number is allowable for use in the V-PLMN. Thismay involve checking a list of designated called party numbers, policiesor agreements with particular roaming partners that indicate the calledparty number may be used for a called party or service within V-PLMN101. The database 105 sends its results/indication to the network node103. On receiving the indication that the called party number (e.g. 133)is an allowable called party number e.g. it may be a local servicenumber, the network node 103 manipulates the SIP signaling (e.g. the SIPINVITE request message) at this point to ensure that H-PLMN 102 receivessufficient information to recognise the originating call as a V-PLMNservice or call to a called party in the V-PLMN.

Manipulating the SIP signaling may be implemented by modifying the SIPINVITE request message associated with the originating call by changingthe phone-context (e.g. geo-local.hoplmn@v-as.vplmn.com) such that theH-PLMN 102 will route the call back to the V-PLMN 101 for processing.Additionally, an indication or routing parameter may be set such thatthe H-PLMN 101 will recognize the originating call should be routed thecall back to the V-PLMN 101 may be inserted into the SIP signaling. Thismay also be accomplished by modifying the parameters of the R-URI of theSIP INVITE request message. Alternatively, the body of the SIP INVITErequest message may be modified with additional informational elementsthat the H-PLMN 102 may be configured to recognize as requiring the callto be routed back to the V-PLMN 101.

On receipt of the modified SIP signaling (e.g. SIP INVITE(113;Phone-Context:geo-local.hplmn.com@v-as.vplmn.com; P-Asserted-ID:<IMPU>)) at the IMS network of HPLMN 102 (e.g. CSCF 108, DNS and MMTel &SCC AS nodes), the IMS nodes of the HPLMN 102 recognise that the callshould be routed back to the V-PLMN 101 such that the call isreturned/routed to VPLMN 101 via the appropriate SIP signaling (e.g. SIPINVITE(113; Phone-Context:geo-local.hplmn.com@v-as.vplmn.com;P-Asserted-ID: <tel: ...>; P-Asserted-ID: <sip:userpart@hplmn.com...>))for further service execution (i.e. call termination with the calledparty) in the IMS nodes (e.g. V-As and/or TRF/CSCF) of VPLMN 101.

In particular, a network node of the H-PLMN 102 e.g. the CSCF 108 (whichmay have the functionality of a P-CSCF or IBCF of the H-PLMN 102) may beconfigured to receive the SIP INVITE request message associated with theoriginating call (e.g. SIP INVITE(113;Phone-Context:geo-local.hplmn.com@v-as.vplmn.com; P-Asserted-ID:<IMPU>)). The SIP INVITE request message including the called partynumber (e.g. 113) associated with the call and an indication (e.g.Phone-Context:geo-local.hplmn.com@v-as.vplmn.com; P-Asserted-ID:<IMPU>)) that the called party number is allowable for use in the V-PLMN101. The network node 108 is configured to detect the indication withinthe received SIP INVITE request message that the called party number isallowable for use in the V-PLMN 101. This may involve conferring withother IMS nodes such as the DNS and MMTel & SCC AS nodes in relation torouting policies or other issues regarding the originating call. Thenetwork node then transmits the received SIP INVITE request message backtowards the V-PLMN 101 (e.g. SIP INVITE(113;Phone-Context:geo-local.hplmn.com@v-as.vplmn.com; P-Asserted-ID: <tel:...>; P-Asserted-ID: <sip:userpart@hplmn.com...>)), which as beenappropriately modified such that the V-PLMN 101 may act accordingly andperforming the terminating call set-up signalling towards the calledparty or service at the terminating side of the call within V-PLMN 101.The SIP INVITE message transmitted from the H-PLMN 102 towards theV-PLMN 101 may be routed to an anchor point such as a Transit RoamingFunction (TRF)/CSCF node 109 and/or a visiting AS (V-AS) (and othernodes) for call processing followed by performing the terminating callset-up signalling towards the called party or service at the terminatingside of the call within V-PLMN 101.

FIG. 1 c is a schematic illustration of various example interfaces forallowing the network node 103 according to the invention to trigger oraccess one or more storage mediums, databases or database servers. Forsimplicity, by way of example only, FIG. 1 c illustrates a database 105based on a database server (DB server) that is provisioned with aplurality of called party numbers. The terms access network and VPLMN101 are used interchangeably and database or database server are alsoused interchangeably. The structure of the database 105 may arrangedsuch that the plurality of called party numbers include a plurality ofservice numbers in the form of records, tables or lists of called partynumbers or any other suitable form of data or database structure. Thedatabase 105 may further include data representative of an indication ofwhether the called party numbers are allowable or not. Alternatively ofin addition, the database 105 may include policies or agreements withthird parties (e.g. other network operators) indicating a set of calledparty numbers or service numbers are allowable and/or not allowable foruse in the access network (VPLMN 101).

The interface from the network node 105 (e.g. a P-CSCF or IBCF) towardthe database 105 may be based on any suitable access/query language oraccess/communications protocol for use in querying the database 105 ordirectory system of the database 105. For example, the interface formthe network node 103 toward the database 105 may be based on suitableprotocols such as Lightweight Directory Access Protocol (LDAP),Diameter, or even SIP and SDP messaging protocols for accessing/queryingthe database 105 and receiving responses from the database 105. In FIG.1 a several alternative direct interfaces based on LDAP are depicted byalternative A1a or alternatives A1b and A2 may be based on aDiameter/SIP interface. Alternative A2 is based on Diameter/SIPinterface that is linked toward an IWF (Interworking Function), whichmay convert the Diameter/SIP protocol into the appropriate protocol foraccessing/querying and receiving responses from the database system ofdatabase 105, which may be, for example, an LDAP DB or a database 105linked with a Service Control Point (SCP) etc. The database 105 may bean internal database of network node 103 or an external database (it mayeven be located in another access network) and provisioned with calledparty numbers allowable for use in the V-PLMN 101 or access network,which may be in the form of policies, dialing plans for the V-PLMN 101or agreements between V-PLMN 101 and HPLMN 102 or other access networks,H-PLMNs and/or VPLMNs.

The network node 103 queries, using a suitable protocol, the database105 as to whether the called party number is allowable for use in theaccess network or VPLMN 101. This may be performed by the network node103 accessing or triggering the database 105 to indicate whether thecalled party number is allowable for use in the access network 101 basedon the data in the database 105. The network node 103 may receive aresponse from the database 105 indicating whether the called partynumber is allowable for use in the access network 101. At the networknode 103, the received response from the database 105 or database server105 may be analysed to determine whether the called party number isallowable for use in the access network 101. However, the response fromthe database 105 may be in the form of a message that includes apositive or negative indication of whether the called party number isallowable.

By way of example only, LDAP may be used for querying data structureswithin the database 105 or database server 105, where both queries tothe database 105 and responses from the database 105 are based on theactual data stored in the database 105. An LDAP query may be an LDAPSearch including the short number or the called party number received inthe SIP INVITE request message. If the called party number is found, anLDAP response may include associated information elements such as thecalled party number and other information associated with the calledparty number (e.g. 1234, PIZZA, complete number=+46xxxxxx). If thecalled party number is not found, then a response such as an LDAP errormay be returned, which may take the form “distinguished name not found”or any other informational or descriptive element and the like. Forother suitable protocols such as Diameter, SIP and/or SDP messaging thedatabase 105 or database server 105 may be configured to provide a moreexplicit response (e.g. “local number” or even “set a phone contextparameter to the access network domain name”) that depends on the typeof query.

Although the network node 103 queries the database 105 and receives aresponse that may indicate whether the called party number is allowablefor use in the access network, it is to be appreciated by the personskilled in the art that the network node 103 can be configured forreceiving any type of response from the database 105 or a databaseserver 105 or any other storage media or suitable system andinterpreting or analysing that response to determine whether the calledparty number is allowable for use in the access network 101 (VPLMN).

FIG. 2 a is a flow diagram illustrating an example process 200 accordingto the invention for routing an originating call from a first UE (e.g.calling party A) in an access network (e.g. V-PLMN 101) including an IMSnetwork, in which the IMS network includes a network node for performingthe process. The steps performed are as follows:

-   201. Receiving, at the network node, a SIP INVITE request message    associated with the originating call from the first UE. The SIP    INVITE request message includes a called party number associated    with the call. The SIP INVITE request message may also include a    home domain name associated with the first UE.-   202. Determining whether the first UE is visiting the access    network. If the first UE is determined to be visiting the access    network, then proceed to step 204. Otherwise proceed to step 203.-   203. Process the SIP INVITE request message using normal call    handling procedures. This is because the first UE is not a visiting    the access network and so is not an IMS inbound roamer.-   204. Determining whether the called party number is associated with    the access network. This may include determining if the called party    number is a short number or a short code number or is a called party    number that is not in a normalised format such as the international    format. If the called party number is associated with the access    network, then proceed to step 205. Otherwise proceed to step 208.-   205. Querying a database, the database including a plurality of    called party numbers, as to whether the called party number is    allowable for use in the access network when the first UE is    visiting the access network and when the called party number is    associated with the access network. Proceed to step 206.-   206. Determining if the called party number is allowable. This may    include receiving a response message or indication from the database    indicating the called party number is allowable. If the called party    number is allowable then proceeding to step 207. Otherwise, proceed    to step 208.-   207. Instructing a home network of the first UE (e.g. an H-PLMN for    the first UE) to route the originating call to the access network    when a response from the query indicates the called party number is    allowable for use in the access network. Proceed to finish of    process or enter a wait state for the next SIP INVITE request    message or response from the home network of the first UE.-   208. Send the SIP INVITE request message towards the home network in    the usual manner. This is because the called party number may not be    allowable in the access network (e.g. not allowed due to roamer    partner agreements/policies or the called party number is not    recognised from the list of allowable called party numbers, etc.)

Step 202 may further determining whether the first UE is IMS registeredand/or determining whether the home network is known to the networknode. Step 204 may further include determining that the called partynumber is representative of a short code number or a short number.

The database may be provisioned with a plurality of called party numbersthat may include a plurality of service numbers and/or policies orroamer agreements indicating whether the plurality of service numbers orother called party numbers are allowable for use in the access network.

Step 205 may further include triggering the database to indicate whetherthe called party number is allowable for use in the access network basedon the service numbers, policies, and/or agreements. This may involve asimple match in the database between the called party number and thecalled party number stored in the database that is allowable.

Step 206 may then further include receiving a response from the databaseindicating whether the called party number is allowable for use in theaccess network. Steps 206 and/or 207 may further include determiningfrom the received response from the database whether the called partynumber is allowable for use in the access network, and instructing thehome network of the first UE to route the originating call to the accessnetwork when it is determined that the called party number is allowablefor use in the access network.

Step 207 may further include modifying the received SIP INVITE requestmessage to set a phone context parameter to the access network domainname when the called party number is allowable for use in the accessnetwork. The modified SIP INVITE message is then transmitted towards thehome network. The phone context parameter may be within the R-URI of theSIP INVITE request message, which is then modified accordingly.

In other embodiments or alternatives, step 207 may include furthermodifying the received SIP INVITE request message to set a routingindication for routing the originating call from the home network to theaccess network when the called party number is allowable for use in theaccess network. The routing indication may be recognised by the homenetwork such that the home network routes the SIP INVITE request messagetowards the access network. The routing indication may be within thebody of the SIP INVITE request message or any other part of the SIPINVITE request message. In some implementations, the R-URI of the SIPINVITE request message may be modified to set the routing indication. Arouting indication may include data representative of routinginstructions for the transmission of the originating call to its finaldestination e.g. the called party or the access network of the calledparty. For example, it may be included in a message header as an addressor a group of characters, which specify routing instructions for thetransmission of the message towards its final destination. As anotherexample, a routing indication may include data representative of a flagor an instruction that indicates to the home network that theoriginating call should be routed towards the access network that thecalled party is visiting, or any other network for that matter.

Although the network node may include the functionality of a P-CSCF orthe functionality of an IBCF, it is to be appreciated by the personskilled in the art that any IMS network node that is suitable forperforming the processes/mechanisms according to the invention.

FIG. 2 b is a flow diagram illustrating an example process 202 performedat the network node for determining 210 whether the first UE is visitingthe access network. The following steps are performed.

-   211. Determine whether the first UE is IMS registered. If the    network node includes the functionality of a P-CSCF or IBCF, then it    can detect this in the usual fashion. Otherwise, the network node    may need to query a node with P-CSCF functionality or even query the    HSS of the home network. If the first UE is IMS registered then    proceed to step 213. If the first UE is not IMS registered, then    proceed to step 212.-   212. As the first UE is not IMS registered, it does not require the    routing mechanism according to the invention. Proceed to step 203 of    FIG. 2 a.-   213. Determine if the first UE is IMS registered toward a home    network different to the access network. This is to determine    whether the first UE is a visiting UE or an IMS roamer. If the first    UE is IMS registered to the home network, then proceed to step 214.    Otherwise, proceed to step 212.-   214. Determine if the home network is known to the access network.    If the home network is not known to the access network, then the    access network will not be able to route the call appropriately. If    the home network is known to the access network, then proceed to    step 215. Otherwise, proceed to step 212.-   215. Proceed to step 204 of FIG. 2 a.

Step 214 may be modified to perform a check to determine if the accessnetwork (visiting network or VPLMN-A) that the first UE (e.g. callingparty) is visiting and the home network of the first UE have anyagreement as to how calls are allowed to be set-up or routed. Inaddition, the determination may further include checking whether thehome network routing policies or implementation is compatible with themethod for routing the originating call according to the invention asimplemented in the access network (VPLMN).

FIG. 2 c is a flow diagram illustrating an example process 204 performedat the network node for determining 220 whether the called party numberis associated with the access network. The following steps areperformed.

-   221. Determine whether the called party number is in the    international format or other standardised format that indicates the    originating call is not meant to be used in the access network. If    the called party number is in the international format (or other    standardised format) then proceed to step 222. Otherwise proceed to    step 223.-   222. As the called party number is meant to be used in another    access network, proceed to step 208 of FIG. 2 a.-   223. Determine whether the called party number is in a short code    format or a short number format. This indicates the called party    number may be allowed to be used in the access network. If the    called party number is in a short code format (or short number    format), then proceed to step 225. Otherwise proceed to step 224.-   224. Proceed to step 205 of FIG. 2 a. This is the step of querying    the database to determined whether the called party number is    actually allowable for use in the access network.-   225. Determine whether the called party number is in any other    format that may be allowed by the access network. This indicates the    called party number may be allowed to be used in the access network.    If the called party number is in another format that may be    allowable for use in the access network, then proceed to step 224.    Otherwise proceed to step 222.

FIG. 2 d is a flow diagram illustrating various examples of process 207that may be performed at the network node when instructing 230 the homenetwork to route the originating call to the access network. Thefollowing steps are performed.

-   231. Modifying the SIP INVITE request message associated to the    originating call to indicate to the home network that the    originating call should be routed back to the access network.    Proceed to step 235.-   235. Transmit the modified SIP INVITE request message towards the    home network.-   and/or-   232. Modifying the SIP INVITE request message associated to the    originating call to indicate to the home network that the    originating call should be routed back to the access network. The    modification includes setting the phone-context parameter in the SIP    INVITE request message to the access network domain name. Proceed to    step 235.-   235. Transmit the modified SIP INVITE request message towards the    home network.-   and/or-   233. Modifying the SIP INVITE request message associated to the    originating call to indicate to the home network that the    originating call should be routed back to the access network. The    modification includes setting a routing indication for routing the    originating call from the home network to the access network.    Proceed to step 235.-   235. Transmit the modified SIP INVITE request message towards the    home network.-   and/or-   233. Modifying the SIP INVITE request message associated to the    originating call to indicate to the home network that the    originating call should be routed back to the access network. The    modification includes modifying the R-URI for setting a routing    indication for routing the originating call from the home network to    the access network. Proceed to step 235.-   235. Transmit the modified SIP INVITE request message towards the    home network.

Although each of the above examples of instructing the home network toroute the originating call to the access network may be performedindividually, it is to be appreciated by a person skilled in the artthat any one of more of these examples may be combined in accordancewith the invention.

FIG. 2 e is a flow diagram illustrating an example process 240 accordingto the invention for routing an originating call from a first UE (e.g.calling party A) in an access network (e.g. V-PLMN 101) including afirst IMS network towards a home network (e.g. H-PLMN 102) including asecond IMS network. The first IMS network including a first network node(e.g. P-CSCF 103) in the access network the first UE is visiting (e.g.V-PLMN 101). The second IMS network including a second network node(e.g. CSCF 108) in the home network of the first UE. The following stepsare performed at the second network node:

-   241. Receiving a SIP INVITE request message associated with the    originating call from the first UE in the visited access network.    The SIP INVITE request message including a called party number    associated with the call and an indication that the called party    number is allowable for use in the visited access network.-   242. Detecting the indication within the received SIP INVITE request    message that the called party number is allowable for use in the    visited access network. If there is an indication that indicates the    called party number is allowable for use in the visited access    network then proceed to step 244. Otherwise proceed to step 243.-   243. Process the originating call according to normal call routing    procedures.-   244. Transmits the received SIP INVITE request message towards the    visited access network. This may involve modifying the received SIP    INVITE request message accordingly, so the visited access network    recognises it appropriately and acts accordingly.

FIG. 3 a is a schematic illustration of a network node 300 for use inrouting an originating call from a first UE or calling party in anaccess network comprising an IMS network. The network node 300 includesa receiver 302, a transmitter 304, a memory unit 306, and processinglogic 308, the processing logic 308 being connected to the receiver 302,to the transmitter 304, and to the memory unit 306.

In operation, the receiver 302 is configured to receive a SIP INVITErequest message associated with the originating call from the first UE.The SIP INVITE request message includes a called party number associatedwith the call. The SIP INVITE request message may also include a homeaccess domain name. The processing logic 308 includes determining logic310 that is configured to determine whether the first UE is visiting theaccess network and to determine whether the called party number isassociated with the access network. The processing logic 308 furtherincludes query logic 312 configured to query a database (not shown), thedatabase including a plurality of called party numbers, as to whetherthe called party number is allowable for use in the access network whenthe determining logic 310 determines that the first UE is visiting theaccess network and that the called party number is associated with theaccess network. The transmitter 304 is configured to send the query tothe database. The processing logic 308 and the transmitter 304 arefurther configured to instruct a home network of the first UE to routethe originating call to the access network when a query response fromthe database indicates that the called party number is allowable for usein the access network.

The determining logic 310 may be further configured to determine whetherthe first UE is IMS registered for use in determining whether the firstUE is visiting the access network. The determining logic 310 may befurther configured to determine whether the home network is known to thenetwork node when the first UE is determined to be visiting the accessnetwork. The determining logic 310 for determining whether the calledparty number is associated with the access network is further configuredto determine that the called party number is representative of a shortcode number or a short number.

The database may be arranged such that the plurality of called partynumbers include a plurality of service numbers, and the databaseincludes records, tables or lists of called party numbers that areallowable or not, or policies or agreements indicating whether theplurality of called party numbers or service numbers are allowable foruse in the access network.

The transmitter 304 and query logic 312 are further configured totrigger the database to indicate whether the called party number isallowable for use in the access network based on the data in thedatabase. The receiver 302 and the processing logic 308 are furtherconfigured to receive a response from the database indicating whetherthe called party number is allowable for use in the access network. Thedetermining logic 310 or other logic may be further configured todetermine, from the received response from the database, whether thecalled party number is allowable for use in the access network. Based onthis determination the processing logic 308 and the transmitter 304 arefurther configured to instruct the home network of the first UE to routethe originating call to the access network when the determining logic310 indicates that the called party number is allowable for use in theaccess network.

The processing logic 308 may be further configured to instruct the homenetwork by modifying the received SIP INVITE request message to set aphone context parameter to the access network domain name when thecalled party number is allowable for use in the IMS network. Thetransmitter 304 may be further configured to instruct the home networkby transmitting the modified SIP INVITE request message towards the homenetwork. In addition or alternatively, the phone context parameter maybe modified within the Request-Uniform Resource Identifier, R-URI, ofthe SIP INVITE request message.

In addition or alternatively, the processing logic 308 may be furtherconfigured to instruct the home network by further modifying thereceived SIP INVITE request message to set a routing indication forrouting the originating call from the home network to the access networkwhen the called party number is allowable for use in the access network.Additionally or alternatively, the processing logic 308 is furtherconfigured to modify the R-URI of the SIP INVITE request message to setthe routing indication.

The network node 300 may include the functionality of a P-CSCF node oran IBCF.

FIG. 3 b is a schematic illustration of a network node 320 for use inrouting an originating call from a first UE or calling party in anaccess network comprising a first IMS network towards a home networkincluding a second IMS network. The first IMS network includes a firstnetwork node 300 associated with the access network the first UE isvisiting. The second IMS network includes the network node 320, which isassociated with a home network of the first UE. The network node 320includes a receiver 322, a transmitter 324, a memory unit 326, andprocessing logic 328, the processing logic 328 being connected to thereceiver 322, to the transmitter 324, and to the memory unit 326.

In operation the receiver is configured to receive a SIP INVITE requestmessage associated with the originating call from the first UE in thevisited access network. The SIP INVITE request message being transmittedfrom the second network node 300. The SIP INVITE request messageincluding a called party number associated with the call and anindication that the called party number is allowable for use in thevisited access network. The processing logic 328 is configured to detectthe indication within the received SIP INVITE request message that thecalled party number is allowable for use in the visited access network.If it is determined that the called party number is allowable for use inthe visited access network, the transmitter 324 and processing logic 328are configured to transmit the SIP INVITE request message towards thevisited access network.

The network node 320 may include the functionality of a P-CSCF node oran IBCF. The network nodes 300 and/or 320 as herein described caninclude memory units 306 and 326 and processing logics 308 and 328,which can be used for storing and executing a computer program,comprising computer readable code which, when executed by the processinglogics 308 and 328, respectively, causes the network node(s) 300 and/or320 to perform the relevant methods, procedures, or processes of theinvention as described herein. Such computer programs as describedherein can be incorporated within one or more computer program products,each comprising a computer readable medium and one or more of thecomputer programs, where one or more of the computer programs are storedon the computer readable medium.

It will be appreciated by the person of skill in the art that variousmodifications may be made to the above described examples and/orembodiments without departing from the scope of the present invention.

1. A method of routing an originating call from a first user equipment,UE, in an access network comprising an Internet Protocol MultimediaSubsystem, IMS, network, wherein the IMS network includes a networknode, the method, performed by the network node, comprising the stepsof: receiving a SIP INVITE request message associated with theoriginating call from the first UE, the SIP INVITE request messageincluding a called party number associated with the call; determiningwhether the first UE is visiting the access network and whether thecalled party number is associated with the access network; querying adatabase, the database comprising a plurality of called party numbers,as to whether the called party number is allowable in the access networkwhen the UE is visiting the access network and when the called partynumber is associated with the access network; and instructing a homenetwork of the first UE to route the originating call to the accessnetwork when a response from the query indicates the called party numberis allowable for use in the access network.
 2. The method according toclaim 1, wherein the step of determining whether the first UE isvisiting the access network further comprises determining whether thefirst UE is IMS registered.
 3. The method according to claim 1, whereinthe step of determining whether the first UE is visiting the accessnetwork further comprises determining whether the home network is knownto the network node.
 4. The method according to claim 1, wherein thestep of determining whether the called party number is associated withthe access network further comprises determining that the called partynumber is representative of a short code number or a short number. 5.The method according to claim 1, wherein the plurality of called partynumbers include a plurality of service numbers, and the databaseincludes policies indicating whether the plurality of service numbersare allowable for use in the access network, the step of determiningfrom the database further comprising: triggering the database toindicate whether the called party number is allowable for use in theaccess network based on the policies; and receiving a response from thedatabase indicating whether the called party number is allowable for usein the access network.
 6. The method according to claim 5, furthercomprising the steps of determining, from the received response from thedatabase, whether the called party number is allowable for use in theaccess network, and instructing the home network of the first UE toroute the originating call to the access network when it is determinedthat the called party number is allowable for use in the access network.7. The method according to claim 1, wherein the step of instructing thehome network further comprises: modifying the received SIP INVITErequest message to set a phone context parameter to the access networkdomain name when the called party number is allowable for use in theaccess network; and transmitting the modified SIP INVITE request messagetowards the home network.
 8. The method according to claim 7, whereinthe phone context parameter is within the Request-Uniform ResourceIdentifier, R-URI, of the SIP INVITE request message.
 9. The methodaccording to claim 7, wherein the step of instructing the home networkfurther comprises modifying the received SIP INVITE request message toset a routing indication for routing the originating call from the homenetwork to the access network when the called party number is allowablefor use in the access network.
 10. The method according to claim 9,wherein the step of modifying the SIP INVITE request message furtherincludes modifying the R-URI of the SIP INVITE request message to setthe routing indication.
 11. The method according to claim 1, wherein thenetwork node includes the functionality of a proxy call session controlfunction or the functionality of an interconnection border controlfunction.
 12. A network node for routing an originating call from afirst user equipment, UE, in an access network comprising an InternetProtocol Multimedia Subsystem, IMS, network, the network nodecomprising: a receiver, a transmitter, a memory unit, and processinglogic, the processing logic being connected to the receiver, to thetransmitter, and to the memory unit wherein: the receiver is configuredto receive a SIP INVITE request message associated with the originatingcall from the first UE, the SIP INVITE request message including acalled party number associated with the call; the processing logiccomprises determining logic configured to determine whether the first UEis visiting the access network and to determine whether the called partynumber is associated with the access network; the processing logicfurther comprising query logic configured to query a database, thedatabase comprising a plurality of called party numbers, as to whetherthe called party number is allowable in the access network when thedetermining logic determines that the first UE is visiting the accessnetwork and that the called party number is associated with the accessnetwork; the transmitter is configured to send the query to thedatabase; and the processing logic and the transmitter are furtherconfigured to instruct a home network of the first UE to route theoriginating call to the access network when a query response from thedatabase indicates that the called party number is allowable for use inthe access network.
 13. The network node according to claim 12, whereinthe determining logic is further configured to determine whether thefirst UE is IMS registered for use in determining whether the first UEis visiting the access network.
 14. The network node according to claim12, wherein the determining logic is further configured to determinewhether the home network is known to the network node when the first UEis determined to be visiting the access network.
 15. The network nodeaccording to claim 12, wherein the determining logic for determiningwhether the called party number is associated with the access network isfurther configured to determine that the called party number isrepresentative of a short code number or a short number.
 16. The networknode according to claim 12, wherein the plurality of called partynumbers include a plurality of service numbers, and the databaseincludes policies indicating whether the plurality of service numbersare allowable for use in the access network, wherein: the transmitterand query logic are further configured to trigger the database toindicate whether the called party number is allowable for use in theaccess network based on the policies; and the receiver and theprocessing logic are further configured to receive a response from thedatabase indicating whether the called party number is allowable for usein the access network.
 17. The method according to claim 16, wherein thedetermining logic is further configured to determine, from the receivedresponse from the database, whether the called party number is allowablefor use in the access network; and the processing logic and thetransmitter are further configured to instruct the home network of thefirst UE to route the originating call to the access network when thedetermining logic indicates that the called party number is allowablefor use in the access network.
 18. The network node according to claim12, wherein the processing logic is further configured to instruct thehome network by modifying the received SIP INVITE request message to seta phone context parameter to the access network domain name when thecalled party number is allowable for use in the IMS network; and thetransmitter is further configured to instruct the home network bytransmitting the modified SIP INVITE request message towards the homenetwork.
 19. The network node according to claim 18, wherein the phonecontext parameter is within the Request-Uniform Resource Identifier,R-URI, of the SIP INVITE request message.
 20. The network node accordingto claim 18, wherein the processing logic is further configured toinstruct the home network by further modifying the received SIP INVITErequest message to set a routing indication for routing the originatingcall from the home network to the access network when the called partynumber is allowable for use in the access network.
 21. The methodaccording to claim 20, wherein the processing logic is furtherconfigured to modify the R-URI of the SIP INVITE request message to setthe routing indication.
 22. The network node according to claim 12,wherein the network node comprises the functionality of a proxy callsession control function or the functionality of an interconnectionborder control function.
 23. A method of routing an originating callfrom a first user equipment, UE, in an access network comprising anInternet Protocol Multimedia Subsystem, IMS, network, wherein the IMSnetwork includes a first network node in an access network the first UEis visiting and a second network node in a home network of the first UE,the method, performed by the second network node, comprising the stepsof: receiving a SIP INVITE request message associated with theoriginating call from the first UE in the visited access network, theSIP INVITE request message including a called party number associatedwith the call and an indication that the called party number isallowable for use in the visited access network; detecting theindication within the received SIP INVITE request message that thecalled party number is allowable for use in the visited access network;and transmitting the SIP INVITE request message towards the visitedaccess network.
 24. A network node for use in routing an originatingcall from a first user equipment, UE, in an access network comprising anInternet Protocol Multimedia Subsystem, IMS, network, wherein the IMSnetwork includes a first network node in an access network the first UEis visiting and the network node is associated with a home network ofthe first UE, the network node comprising: a receiver, a transmitter, amemory unit, and processing logic, the processing logic being connectedto the receiver, to the transmitter, and to the memory unit, wherein:the receiver is configured to receive a SIP INVITE request messageassociated with the originating call from the first UE in the visitedaccess network, the SIP INVITE request message including a called partynumber associated with the call and an indication that the called partynumber is allowable for use in the visited access network; theprocessing logic is configured to detect the indication within thereceived SIP INVITE request message that the called party number isallowable for use in the visited access network; and the transmitter andprocessing logic are configured to transmit the SIP INVITE requestmessage towards the visited access network.